Improving DNA recovery of low copy samples from handguns

            Handguns are one of the most commonly used weapons in US crimes.  Collecting DNA evidence from handguns poses many challenges such as degradation, stability, and inhibition.  In this study we determined whether a new sampling method improved the recovery and stability of DNA from these types of samples.  The four metals associated with handguns we used in this study were stainless steel, brass, aluminum, and galvanized stainless steel.  The three different swabs we used to compare recovery were DNA sterile cotton swabs, DNA free cotton swabs, and foam tipped DNA free swabs from Puritan (Guilford, ME).  We first created an elimination database to be able to detect contamination that may have derived from laboratory staff.  Then we created a cleaning process to recover cellular DNA from the metals.  To determine whether DNA contamination was present on the swabs and to determine the effectiveness of our cleaning process, control samples were assessed by qPCR. Saliva was deposited on the metals and then collected using the different swabs.  DNA was extracted using the organic extraction process, quantified with qPCR, typed by PCR STR multiplex amplification, and capillary electrophoresis.  GeneMapper ID from Applied Biosystems (Foster City, CA) was used to evaluate the data.  A low level of contamination for the “sterile” cotton swabs was observed.  The results of this study should lead to improved recovery of DNA from handguns.